1. Technical Field of the Invention
The present invention relates to an analog optical transmission system, a Master unit and a Slave unit which transmit analog optical signals from the Master unit to the Slave unit via a downlink optical fiber and also does so from the Slave unit to the Master unit via an uplink optical fiber, and more particularly, to technologies whereby faults occurring on the uplink or downlink optical fiber can be detected by the Master unit or a user who monitors the Master unit, even if the Slave unit should not detect the faults on the downlink optical fiber.
2. Related Art
Optical fibers, for example, are well known as low-loss transmission lines through which optical signals can be transferred and have been utilized in various optical communication fields. Although the optical transmission system utilizing such optical fibers as transmission lines can transfer optical signals efficiently as above-mentioned, a normal optical communication cannot be performed, if transmission is loss is increased or optical signals are interrupted by damage, disconnection, or cut-off on the optical fiber. Thus, in an optical transmission system, the monitor on transmission faults is performed, for example, on real-time about whether damage of optical fibers used as transmission lines are caused or not, and such monitoring is very important from the point of system reliability.
In the optical transmission system that transmits respective optical signals from the Master unit to the Slave unit via a downlink optical fiber and from the Slave unit to: the Master unit via an uplink optical fiber, the communication is performed using a communication circuit for control between a CPU of a microcomputer or the like equipped in the Master unit and a CPU of a microcomputer or the like equipped in the Slave unit so that the Master unit monitors states of each processing section of the Slave unit and controls the gain thereof.
In the analog optical transmission systems with such a configuration, the Master unit, for example, monitors the uplink optical fiber, while the Slave unit monitors the downlink optical fiber. If a fault of the downlink optical fiber is detected, the Slave unit may inform it to the Master unit using the above-mentioned communication circuit. More specifically, in monitoring in the Slave unit, when receiving analog optical signals transmitted from the Master unit via the downlink optical fiber, the CPU always monitors the level of the received light of the concerned light reception element, and if a fault of the downlink optical fiber is detected by the CPU, it may be informed to the CPU of the Master unit.
On the other hand, the Master unit, when notified of the fault of the downlink optical fiber by the Slave unit, outputs a warning alarm of the fault to the user.
However, the above-mentioned analog optical transmission system suffers from such drawback that, although the Master unit can monitor the uplink optical fiber as above-mentioned, the downlink optical fiber must be monitored by the Slave unit and the monitoring results must be informed to the Master unit, thus both the Master and Slave units must monitor the optical fibers.
Specifically, such types of analog optical transmission systems have a drawback of a complicated configuration for monitoring optical fibers, because it is necessary to create communication protocols for, for example, informing the monitoring results from the Slave unit to the Master unit, to provide with both the Master and Slave units control programs to be executed by the CPU for processings of such information and the monitoring of optical fiber, and also to equip the above-mentioned controlling communication circuits. Such drawback is particularly conspicuous in those systems that may not need to execute control between the Master and Slave units besides the above-mentioned optical fiber monitoring and informing processings, and there has been an urgent need for a simple monitoring configuration that allows execution of the monitoring of two-route optical fibers only by, for example, the Master unit.
To solve those problems of the prior arts, the present invention has an object to provide an analog optical transmission system as well as the related Master and Slave units that enable the Master unit or the user who monitors the Master unit to detect faults of the uplink or downlink optical fiber even if there is no need, for example, for the Slave unit to monitor the downlink optical fiber, in such a case where the bilateral communication of analog optical signals is performed by using two-route optical fibers between the Master and Slave units.
An analog optical transmission system according to the present invention is capable of detecting faults of optical fibers as follows when executing the bilateral communication of analog optical signals by use of two-route optical fibers, uplink and downlink, between the Master and Slave units:
That is, while the Master unit has the Master light emission means for transmitting a prescribed monitoring optical signal to the Slave unit via the downlink optical fiber, the Slave unit has the Slave light reception means for receiving the abovementioned monitoring optical signal sent from the Master unit via the downlink optical fiber. The Slave light emission means returns the above-mentioned monitoring optical signals received by the Slave light reception means to the Master unit via the uplink optical fiber. Then, in the Master unit, its light reception means receives the above-mentioned monitoring optical signal returned from the Slave unit via the uplink optical fiber, allowing a monitoring signal-level detection means to detect the level of the above-mentioned monitoring optical signal received by the Master light reception means.
Thus, it is possible to detect faults of the optical fibers based on fluctuations in the level detected by the monitoring signal-level detection means. More specifically, if, for example, the level of the above-mentioned monitoring optical signal detected by the Master unit is lower than a normal reference level, it is possible to determine that a fault occurs at least one of the uplink and downlink optical fibers, so that such a configuration is effective in a case where it is requested only to detect any faults of either the uplink or downlink optical fiber and there is no need to determine which of the two fibers has a trouble.
Moreover, prescribed monitoring optical signals described herein may include any signal depending on the service conditions of, for example, the system as well as the Master or Slave unit.
In addition to the above-mentioned analog optical transmission systems, the present invention provides such Master and Slave units as above-mentioned.
That is, in bilateral communication of analog optical signals by use of two-route optical fibers, uplink and downlink, between a Master and Slave units, the Master unit according to the present invention has its light emission means for transmitting a prescribed monitoring optical signal to the Slave unit via the downlink optical fiber and the Master light reception means receive the above-mentioned monitoring optical signal returned from the Slave unit via the uplink optical fiber. The monitoring signal-level detection means detects the level of the above-mentioned monitoring optical signal received by the Master light reception means, thereby enabling to detect faults of the optical fibers based on the fluctuations in the level detected by the monitoring signal-level detection means.
On the other hand, the Slave unit according to the present invention, when executing bilateral communication of analog optical signals by use of two-route optical fibers, uplink and downlink, between the Master and Slave units, has the Slave light reception means for receiving the prescribed monitoring optical signal transmitted from the Master unit via the downlink optical fiber and the Slave light emission means for returning the above-mentioned monitoring optical signal received by its light reception means to the Master unit via the uplink Optical fiber, thus enabling to detect faults of the optical fibers based on the fluctuations in the level of the above-mentioned monitoring optical signal detected by the Master unit.
Moreover in an analog optical transmission system according to the present invention, it is possible to detect optical fiber faults in bilateral transmission of analog optical signals by use of two-route optical fibers, uplink and downlink, between a Master unit and Slave unit.
That is, the Master unit has the Master light emission means for transmitting an analog optical signal given by multiplexing a prescribed monitoring signal and an information signal to be sent to the Slave unit via the downlink optical fiber. The Slave unit has the Slave light reception means for receiving the analog optical signal sent from the Master unit via the downlink optical fiber so that the Slave filter means separates the above-mentioned monitoring signal from the analog optical signal received by the Slave light reception means and then the Slave light emission means transmits via the uplink optical fiber to the Master unit an analog optical signal obtained by multiplexing an information signal to be sent to the Master unit and the above-mentioned monitoring signal thus separated by the Slave filter means.
On the other hand, on the side of the Master unit, the Master light reception means receives the analog optical signal sent from the Slave unit via the uplink optical fiber and then the Master filter means separates the above-mentioned monitoring signal from the analog optical signal received by the Master light reception means, thus allowing the monitoring signal-level detection means to detect the level of the above-mentioned monitoring signal separated by the Master filter means.
Thus, in much the same way as mentioned above, it is possible to detect optical fiber faults based on fluctuations in the level detected by the monitoring signal-level detection means on the side of the Master unit. In addition, the present invention multiplexes an information signal and the monitoring signal, to make sure that the two would never mix with each other, thus enabling real-time monitoring and fault detection of optical fibers when executing the communication of, for example, the information signal.
Note here that an information signal mentioned herein refers to a signal originally transferred between the Master and Slave units, for example, prior to the application of the present invention, more specifically to a signal containing data information or control information transferred, for example, between the Master and Slave units.
Further, a prescribed monitoring signal mentioned herein refers to any signal depending on the service conditions of, for example, the system as well as the Master and/or Slave units.
Moreover, the above-mentioned analog optical transmission system according to the present invention makes it possible to detect a fault by specifying which of the uplink or downlink optical fibers has an fault as follows.
That is, the light emission means on the side of the Slave unit transmits by a prescribed average optical power analog optical signal multiplexing the above-mentioned monitoring signal and an information signal at a ratio according to a level of the abovementioned monitoring signal received from the Master unit, while the average received-light level detection means on the Master unit detects an average received-light level of the analog optical signal received by the Master light reception means.
Thus, it is possible to detect a fault by specifying which of the uplink or downlink optical fibers has the fault based on the fluctuations in the average received-light level detected by the Master average received-light level detection means as well as fluctuations in the ratio between the above-mentioned average received-light level and the level detected by the monitoring signal-level detection means. More specifically, if, for example, an average received-light level detected by the Master unit is found to be lower than a normal reference level, the uplink optical fiber can be determined to have faults. While if, for example, a ratio of the above-mentioned monitoring signal level to the above-mentioned average received-light level is found to be lower than a normal reference value, the downlink optical fiber can be determined to have faults.
Note here that there are no restrictions on how to multiplex the above-mentioned monitoring signal and an information signal at a ratio according to the level of the above-mentioned monitoring signal received from the Master unit. The Slave unit side can multiplex those signals, thereby the Master unit side may detect optical fiber faults based on, as mentioned above, a ratio of the above-mentioned monitoring signal level to the above-mentioned average received-light level.
Moreover, a prescribed average optical power mentioned herein preferably is, for example, a constant level always, so that in the case where, for example, the average optical power of the analog optical signals sent from the Slave unit to the Master unit would fluctuate is known beforehand, the Master unit can change the reference level depending to these fluctuations so as to detect optical fiber faults accurately even if the above-mentioned average optical power fluctuates with time etc.
Moreover, one aspect allows the user of an analog optical transmission system according to the present invention to determine optical fiber faults as follows.
That is, the Master unit has its output means for outputting the user with the information of a level to be detected by the monitoring signal-level detection means and an average received-light level detected by the average received-light level detection means, thereby enabling the user to determine optical fiber faults based on the information output by the Master output means.
On such a configuration, the user who, for example, operates the Master unit can detect optical fiber faults; more specifically, the Master unit provided with an output means comprising a monitor screen etc. can, for example, display on the above-mentioned monitor screen the detection results by the above-mentioned monitoring signal-level detection means and those by the average received-light level detection means, thus allowing the user monitoring those detection results on the screen etc. to decide whether faults have occurred on optical fibers or not.
Note here that information mentioned herein on the level detected by the monitoring signal-level detection means and the average received-light level detected by the average received-light level detection means may be, for example, a level itself detected or any information to specify the level within a practical effective accuracy; in short, it may be any information as long as it enables detection of the occurrence of optical fiber faults.
Also note that an output means mentioned herein does not only refer to a monitor screen as mentioned above or other output device for outputting by means of characters, numeric characters, or graphics but various output devices such as an audio or optical power device.
In another aspect, the analog optical transmission system according to the present invention notifies the user of optical fiber faults which it has detected as follows.
That is, in the Master unit the fault detection means decides faults of the uplink optical fiber by detecting that an average received-light level detected by the average received-light level detection means has shifted off a reference level, and decides faults of the downlink optical fiber by detecting a ratio of the average received-light level detected by the average received-light level detection means to the level detected by the monitoring signal-level detection means has shifted off a reference value, so that the fault notification means may notify the user of the fault detected by the fault detection means.
On such a configuration, when an optical fiber fault can be detected by, for example, constituting the fault detection means from the CPU or the like of the Master unit, and more specifically by, for example, allowing the CPU etc. to detect a two-route optical, fiber fault based on the detection results by the average received-light level detection means as well as those by the monitoring signal-level detection means, the detection of optical fiber fault can be informed to the user by the fault notification means comprising a buzzer etc.
Note here that a reference level or value mentioned herein refers to, for example, an average received-light level when the optical fiber is normal or a ratio of the average received-light level to a monitoring signal level. The reference level or value can be used to decide an optical fiber fault if the average received-light level or the ratio of the average received-light level to the monitoring signal level has shifted from a reference level or value.
Moreover, the fault detection means utilized in the present invention need not always be composed of such a CPU as mentioned above but in short may be of any configuration as long as optical fiber faults can be detected based on a detected average received-light level or a monitoring signal level.
Furthermore, the fault information means utilized in the present invention is not always restricted to a device such as a buzzer or any other audio device as mentioned above but may be of various configurations of devices by use of characters, images, or lights.
An example of the analog optical transmission system according to the present invention may be a CATV signal repeater system for optical CATVs, utilizing CATV signals as the abovementioned information signal. The CATV signal herein is not restricted to a TV broadcasting signal transmitted from the Master unit installed at the CATV center to Slave units installed at general houses, but includes an on-demand video signal or other control signal transmitted from the Slave unit at the general houses to the Master unit at the CATV center or also may be, for example, an internet signal transferred in bilateral communication by use of cable modems etc.
In the analog optical transmission system related to the present invention, another example may be a repeater system for communication signals of cellular telephones or other mobiles, a mobile communication signal is utilized as the information signal.
Note here that the present invention is not only limited to the above-mentioned fields but can be used in other various fields that involve bilateral communication of analog optical signals by use of uplink and downlink optical fibers.
The present invention herein provides not only the abovementioned analog optical transmission systems but also the abovementioned Master and Slave units.
That is, a Master unit according to the present invention, when executing bilateral communication of analog optical signals by use of two-route optical fibers, uplink and downlink, between itself and a Slave unit, has the Master light emission means for transmitting via the downlink optical fiber to the Slave unit an analog optical signal multiplexing a prescribed monitoring signal and an information signal to be sent to the Slave unit, and also the Master light reception means for receiving via the uplink optical fiber an analog optical signal multiplexing an information signal to be sent to the Master unit and the above-mentioned monitoring signal of the analog optical signal received via the downlink optical fiber from the Master unit by the Slave unit, so that the Master filter means separates the above-mentioned monitoring signal from the analog optical signal received by the Master light reception means and the monitoring signal-level detection means detects the level of the above-mentioned monitoring signal separated by the Master filter means, thus enabling the detection of optical fiber faults based on the fluctuations in the level detected by the monitoring signal-level detection means.
Moreover, on the Master unit according to the present invention, the above-mentioned Master light reception means receives via the uplink optical fiber an analog optical signal multiplexing at a prescribed average optical power both the abovementioned monitoring signal received from the Master unit by the Slave unit and an information signal to be sent to the Master unit at a ratio according to the level of the above-mentioned monitoring signal, and the average received-light detection means detects an average received-light level of the analog optical signal received by the Master light reception means, thus making it possible to detect a fault by specifying which of the uplink and downlink optical fibers has the fault based on the fluctuations in the average received-light level detected by the average received-light detection means and those at the ratio of the above-mentioned average received-light level to the level detected by the monitoring signal level detection means.
Furthermore, in one aspect of the above-mentioned Master unit according to the present invention, the output means outputs to the user the information of both the level detected by the monitoring signal level detection means and the average received-light level detected by the average received-light detection means, thereby enabling the user to detect optical fiber faults based on the abovementioned information provided by the output means.
In another aspect of the above-mentioned Master unit of the present invention, the fault detection means detects a fault of the uplink optical fiber when the fault detection means detects that the average received-light level detected by the average received-light detection means has shifted from a reference level, and also detects faults of the downlink optical fiber when the ratio of the average received-light level detected by the average received-light detection means to the level detected by the monitoring signal-level detection means has shifted from a reference value, thereby enabling the fault notification means to notify the user of faults detected by the fault detection means.
Moreover, in the Slave unit of the present invention, when executing during bilateral communication by use of two-route optical fibers, uplink and downlink, between itself and the Master unit, the Slave light reception means receives via the downlink optical fiber an analog optical signal multiplexing a prescribed monitoring signal and an information signal to be sent to the Slave unit from the Master unit, and the Slave filter means separates the above-mentioned monitoring signal from the analog optical signal received by the Slave light reception means, and the Slave light emission means transmits via the uplink optical fiber to the Master unit an analog optical signal multiplexing the above-mentioned monitoring signal separated by the Slave filter means and an information signal to be sent to the Master unit, thereby making it possible to detect optical fiber faults based on the fluctuations in the level of the above-mentioned monitoring signal contained in the above-mentioned analog optical signal received by the Master unit.
Furthermore, in the Slave unit of the present invention, the above-mentioned Slave light emission means transmits, at a prescribed analog optical power, an analog optical signal multiplexing the above-mentioned monitoring signal and an information signal at a ratio according to the level of the above-mentioned monitoring signal received from the Master unit, thereby making it possible to detect a fault by specifying which of the uplink optical fiber or downlink optical fiber has the fault of the optical fiber based on the fluctuations in the level of the average received light contained in the above-mentioned analog optical signal received by the Master unit and also those in the ratio of the above-mentioned average received-light level to the level of the above-mentioned monitoring signal contained in the above-mentioned analog optical signal.
Besides, in a preferred embodiment of an analog optical transmission system of the present invention, when executing bilateral communication of analog optical signals by use of two-route optical fibers, uplink and downlink, between the Master and Slave units, optical fiber faults can be detected as follows.
That is, the Master unit oscillates a monitoring signal with a frequency different from that of an information signal to be sent to the Slave unit by the oscillator, and the Master composition means synthesizes the information signal to be sent to the Slave unit and the above-mentioned monitoring signal oscillated by the oscillator, thus allowing the Master light emission means to convert the synthesized signal output from the Master composition means into an analog optical signal and transmit it to the Slave unit via the downlink optical fiber.
In the Slave unit on the other hand, the Slave light reception means receives the analog optical signal sent from the Master unit via the downlink optical fiber, and the Slave filter means separates a signal having a frequency in response to the above-mentioned monitoring signal from the analog optical signal received from the Slave light reception means, and the Slave composition means synthesizes the above-mentioned signal separated by the Slave filter means and the information signal to be sent to the Master unit, and then the Slave light emission means converts the synthesized signal output from the Slave composition means into an analog optical signal having a constant average optical power and transmits it to the Master unit via the uplink optical fiber.
In the Master unit on the other hand, the Master light reception means receives an analog optical signal sent from the Slave unit via the uplink optical fiber, and the average received-light level detection means detects the average received-light level of the analog optical signal received by the Master light reception means, and the Master filter means separates a signal having a frequency corresponding to the above-mentioned monitoring signal from the analog optical signal received by the Master light reception means, and then the monitoring signal-level detection means detects the level of the above-mentioned signal separated by the Master filter means.
Thus, it is possible to detect a fault by specifying which of the uplink optical fiber or downlink optical fiber has the fault based on the fluctuations in the level of the average received light detected by the average received-light level detection means and those in the level detected by the monitoring signal-level detection means on the Master. More specifically, for example, if the above-mentioned average received light detected by the Master unit is found to be lower than a normal reference level, the uplink optical fiber can be considered to have an fault; and if the ratio of the above-mentioned monitoring signal level to the above-mentioned average received light detected by the Master unit is found to be lower than a normal reference value, the downlink optical fiber can be considered to have a fault.
Thus, in an analog optical transmission system as well as a Master or Slave unit according to the present invention, even if, for example, the Slave unit does not monitor the downlink optical fiber, the Master unit or the user, for example, who monitors the Master unit can monitor the two-route optical fibers to detect faults. The present invention does not necessarily require both the Master and Slave units to monitor optical fibers, thereby simplifying the monitoring configuration.